Reference is initially made to FIGS. 1 to 4 of the drawings. Integrated power modules (IPM) are, as is generally known in the art, composed of various circuit components including, in particular, power switching devices 10, reverse current circulating diodes 20, a gate driver IC(s) 30 and associated discrete components 40. In a typical construction of the prior art IPM, the power switching devices 10 (typically IGBT or MOSFET) and the reverse current circulating diodes 20 are supported on a ceramic substrate 100, forming a first unit. The gate driver IC(s) 30 and associated discrete components 40 are supported on a printed circuit board (PCB) 200, forming a second unit.
The ceramic substrate 100 (typically aluminium oxide) includes direct bond copper (DBC) 110 and 120 on both sides, with the copper 110 on a first side bearing an etched pattern to provide mounting pads and connections for the power switching devices 10 and the reverse current circulating diodes 20, and the copper 120 on the opposite second side exposed and acting as a heat sink. The power switching devices 10 and the reverse current circulating diodes 20 are in naked die form and are die attached to the ceramic substrate 100, with their substrate sides attached to the DBC copper 110 on the ceramic substrate 100 to produce a power board P, that being the said first unit.
The printed circuit board or PCB 200 is typically provided by a FR4 substrate. The gate driver IC(s) 30 is in the form of a naked die(s) or packaged IC(s), and so are the associated discrete components 40. They are surface mounted on the PCB 200 and are processed with normal electronic manufacturing process to produce a driver board or driver PCBA Q, that being the said second unit.
These two units are then transferred and mounted on to a lead frame 70, where they are electrically connected with their circuit components interconnected by electrical connections typically making use of bond wires 50, such as bond wires 51 between the power switching devices 10 and the reverse current circulating diodes 20 on the power board P, bond wires 52 between the power board P and the driver PCBA Q, and bond wires 53 between the power board P and the connection pins 71 on the lead frame 70. Further connection from the gate driver IC(s) 30 to the PCB 200 is needed where the gate driver IC(s) 30 is in the form of a naked die(s).
The two said connected/bonded units on the lead frame 70 are subsequently transferred to a packaging station where they are encased in a semiconductor package 60, with the connection pins 71 extending from the lead frame 70 finally trimmed and formed to complete the production of the IPM (integrated power module).
As is generally known in the art, the power board P and the driver PCBA Q are first mounted on the lead frame 70 for support before electrical interconnections are made through the use of bond wires 50. This bonding process often requires a relatively large number of bonding operations and may involve bond wires of different materials and sizes. This leads to compromise in reliability.
In addition, and of more concern, the fragile bond wires 52 bridging across the power board P and the driver PCBA Q are prone to damage (i.e. breaking) if they are made before, and when, the two interconnected units are transferred to the lead frame 70 for mounting thereon.
As a further problem or shortcoming, it is impossible to perform electrical tests on the IPM circuit prior to moulding of the semiconductor package 60 because all connection pins 71 are uncut and hence short circuited in the lead frame 70 before the lead frame 70 is trimmed and formed to bring about the connection pins 71. This leads to lowering of yield.
The subject invention seeks to mitigate or at least to alleviate these problems or shortcomings by providing a new or otherwise improved integrated power module (IPM) and manufacturing method thereof.